Yeah, practice makes perfect, that's for sure. You should see every old spriter first try, it's a mess, haha.

As for the palettes, you can pick various colors from various sprites, sure. Just make sure once you pick let's say, blues from Black mage, make sure you take all shades of blue(from brightest to darkest), not one or two. As long as you keep this rule on, it will be fine. That's why the darks on your Mime got weird most likely, since you mixed various shades from various sprites, stick to just one sprite next time.

Graphics Gale is my favorite tool, tried Photoshop once, but it ain;t just my drill. Using GG all these years and I still love it

Wanted to go ahead and do some fixes myself, but there are more issues than I thought. Mainly the palette, I erased the portrait, and it was still over 16 colors. Reason she is hard to see on black background is cause darkest shade you have is at 12 value, way too dark.

There are many issues with the sprite, and unless you want it to look on par with the FFT quality, you will need to start over. Pick the base that is suitable(guess you will settle on Meliadoul), then get the palette right, first of all. Palette is essential, without getting it right first, starting the sprite might end up in a mess later on. Pick ONLY colors from existing FFT sprites, that way you can be 100% sure to get colors that won't be saturated or stand out. Never pick your own colors, not after you get some experience at least.

I will be wiling to help you out with the concepting stage, just make sure to get the basic stuff down first.

I looked closer on the sprite, and there are quite a few things to fix. First of all, the detail Toshiko spoke of, you just added a shade at the bottom of the fur, it doesn't really work. Look at Female Animist sprite from JOT5 for perfect reference on that. Second thing is the hair, why is the darker shade inside, and brighter working as an outline? It can't be like that. Another thing is the fur at the end of the coat at back frames, you made chessboard shading, and it doesn't work in FFT style at all. I cannot also tell what's on her legs(the belt design thing from FFX), it's a rather complicated detail, and it won't translate into FFT no matter what you do, simplyfiyng is neccesary.

Still, I advise you use references and copy-paste sprite parts at first, it's easier to get grasp of the basics, and how it all works and looks in FFT. Doing custom parts is almost guaranteed to never work out at the beggining. Hope it helps you, good luck

And, I wanted to make a suggestion too, could you add Dias Flac from Star Ocean: Second Story (PSX)/ Star Ocean: Second Evolution (PSP). I love this character and he almost dont have anything in the games he appear.